We have designed peptides with particular characteristics 1) binding and dissocation rates appropriate for subsecond analysis of macromolecular assembly; 2) introduction of the fluorophore into regions of the receptor binding pocket which undergo conformational changes; and 3) high affinity antagonists to the receptor. We are developing novel peptides which permit simultaneous biochemical, immunological, and fluorescence detection: peptides that can be crosslinked to receptors, detected by flow and fluorescence with fluorescein, and also immunologically by antibodies to fluorescein (manuscript in press). We are exploring the possibility that sensitive detection, as applied to capillary electrophoresis will enable analysis of receptor structure.